Reticle fabrication using a removable hard mask

ABSTRACT

We have reduced the critical dimension bias for reticle fabrication. Pattern transfer to the radiation-blocking layer of the reticle substrate essentially depends upon use of a hard mask to which the pattern is transferred from a photoresist. The photoresist pull back which occurs during pattern transfer to the hard mask is minimalized. In addition, a hard mask material having anti-reflective properties which are matched to the reflective characteristics of the radiation-blocking layer enables a reduction in critical dimension size and an improvement in the pattern feature integrity in the hard mask itself. An anti-reflective hard mask layer left on the radiation-blocking layer provides functionality when the reticle is used in a semiconductor device manufacturing process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method used to fabricate a reticle,which is also commonly referred to as a photomask. The reticle includesa patterned layer through which radiation passes during the transfer ofthe pattern from the reticle to a substrate via photolithographictechniques.

2. Description of the Background Art

A typical reticle fabrication process begins with the formation of asubstrate which typically includes a silicon-containing base layer suchas a quartz layer, with a layer of chrome applied over the quartz, and alayer of chrome oxide transitioning to chrome oxynitride which is formedover the chrome layer. A photoresist material is commonly applied overthe chrome oxide/chrome oxynitride layer. The photoresist material ispattern imaged by irradiation, and the image in the photoresist isdeveloped into a pattern. Then the patterned photoresist is used as amask for transferring the pattern to the chrome layer. The pattern inthe chrome layer permits radiation to pass through portions of thereticle when the reticle is used in the fabrication of a substrate, suchas a semiconductor substrate, where the pattern is transferred viaphotolithography to the semiconductor substrate. The chrome oxide/chromeoxynitride layer of the reticle substrate functions as ananti-reflective coating (ARC) during patterning of the chrome layer.However, the anti-reflective properties of this layer are not aseffective for present day photoresist imaging radiation as they were forimaging radiation which was used with earlier photoresists used in theart of reticle fabrication.

Reticles which are used in combination with a stepper of the kind usedfor semiconductor fabrication are generally 6 inch squares which areabout 0.25 inches thick. Such reticles can be fabricated in most 8 inchor larger processing chambers of the kind which are used to fabricatesemiconductor wafers. However, since the reticle is subsequently used ina manner where imaging radiation will come down through the top and outthe bottom, there cannot be any significant scratches on either surfaceof the reticle through which the radiation will pass. As a result, thetool used for reticle fabrication requires specialized reticle substratehandling devices and contact surfaces. For example, a robot blade whichmoves the reticle substrate may hold it only by the edges or corners ofthe substrate and within a specific distance from the edge of thesubstrate. The pedestal upon which the reticle substrate sits isdesigned for minimal contact with the substrate, where a raised liptouches the edge of the reticle substrate or a few protrusions from thepedestal contact the reticle substrate.

Currently, during formation of the reticle substrate, the quartz baselayer is polished on both major surfaces, followed by physical vapordeposition of a radiation-blocking layer such as a chrome layer over oneof the major surfaces. Toward the end of the deposition of the chromelayer, oxygen is added to the deposition chamber so that a chrome oxideis formed; subsequently a small amount of nitrogen (referred to as anitrogen bleed) is added to the deposition chamber as well, so thatchrome oxide transitions to chrome oxynitride. As previously mentioned,the chrome oxide/chrome oxynitride layer functions to reducereflectivity of the chrome surface during pattern imaging of aphotoresist which is applied over the surface of the chrome oxide/chromeoxynitride layer. The amount of reflectivity depends on the imagingradiation.

One of the preferred direct write tools for imaging the photoresist is acontinuous wave laser which writes at a wavelength of about 257 nm or198 nm. This direct write tool is available under the trademark of ALTA™from ETEC Systems, Inc., Hillsboro, Oreg. The reflectivity of the chromeoxide/chrome oxynitride layer is on the order of about 14% at 257 nm.This is much higher than desired and is an artifact from earliertechniques used to imaging the photoresist, where the imaging wavelengthof the radiation was in the range of 405 nm and this worked incombination with the composition of the chrome oxide/chrome oxynitridelayer to produce a reflectivity on the order of less than about 10%. Tocompensate for the present reflectivity problem during imaging of thephotoresist with the radiation tools used today, an organicantireflective coating (ARC) may be applied over the surface of thechrome oxide/chrome oxynitride layer.

The chrome layer is typically patterned using a plasma dry etchtechnique where the plasma is generated from a source gas of chlorineand oxygen. This plasma etchant tends not to attack the quartz base ofthe substrate, which needs to remain transparent to radiation, so thatthe pattern in the chrome will be properly transferred duringfabrication of a semiconductor wafer, for example but not by way oflimitation. However, while the chlorine/oxygen plasma does not attackthe quartz base of the reticle substrate, the oxygen present in theplasma does attack the photoresist which is being used to transfer thepattern to the chrome layer. This causes faceting of the photoresist,which is commonly referred to as “resist pull back”, where the change inthe critical dimension written into the photoresist is reflected in achange in the critical dimension of a pattern etched into the chrome.This is sometimes referred to as “CD loss”. For example, based on acurrent test pattern where the nominal feature size pattern in thephotoresist is about 720 nm, the feature size produced in the chrome maybe 60 nm to 70 nm larger, principally due to resist pull back effects.If, for example, and not by way of limitation, the smallest space thatcan be written on a typical ARF (193 nm) photoresist using a 198 nmwavelength continuous wave laser is in the range of about 110 nm, thendue to the resist pull back, the smallest chrome space which can bewritten may be in the range of about 170 nm to 180 nm. If, for example,and not by way of limitation, the smallest space that can be written ona typical ARF (193 nm) photoresist using an e-beam writing tool,available from Toshiba or Hitachi, for example, is about 90 nm, then dueto the resist pull back, the smallest chrome space which can be writtenbecomes about 150 nm to 160 nm. It is readily apparent that if thisphotoresist pull back problem can be eliminated, the smallest chromefeature which can be obtained is substantially improved.

The importance of eliminating the photoresist pull back problem is evenmore important when phase shifting reticles are considered. At presentthese reticles make up about 25% of reticles produced, but thispercentage is increasing as feature dimension requirements go to smallerfeature sizes. Phase shifting reticles are designed to neutralizediffraction components of the imaging radiation which affects the widthof the space which can be written in the chrome. One of the preferredmethods of phase shifting is accomplished using diffraction slits atparticular locations in the chrome pattern. For a binary mask where thesmallest space which can be written is 100 nm, for example, the phaseshifting slit would preferably be in the range of 30 nm. However, since30 nm cannot be written, the phase shift is limited to the threshold ofwhat can be written. By eliminating the photoresist pull back(eliminating the CD bias which occurs because of the resist pull back),then the threshold for phase shifting can be lowered, and the featureresolution and integrity can be improved.

U.S. Pat. No. 6,171,764 to Ku et al., issued Jan. 9, 2001 describes thekinds of radiation reflection problems which may occur inphotolithographic processes. The description relates to semiconductormanufacturing processes which make use of a dielectric anti-reflective(DARC) layer to reduce reflected radiation during photoresist imaging.In particular, the difference between the Ku et al. invention and otherknown methods is based on the ordering of specific layers in thesubstrate used in the photolithographic process. In the Ku et al.method, the DARC layer is applied over a substrate, followed by a hardmask layer, and then a photoresist. This is said to compare with otherknown methods where the DARC layer is used between the photoresist layerand the hard mask layer. (Col. 3, lines 35-46.)

U.S. Pat. No. 6,607,984 to Lee et al., issued Aug. 19, 2003 describes amethod of semiconductor fabrication in which an inorganicanti-reflection coating is employed and subsequently removed byselective etching relative to an underlying inorganic dielectric layer.(Col. 1, lines 61-67, continuing at Col. 2 lines 1-6.)

European Patent Application No. 99204265.5 of Shao-Wen Hsia et al.,published Jun. 21, 2000, describes a semiconductor interconnectstructure employing an inorganic dielectric layer produced by plasmaenhanced chemical vapor deposition (PECVD). In accordance with apreferred embodiment of the invention, a metal layer upon whichphotoresist patterns are developed comprises a sandwiched metal stackhaving a layer of conducting metal (aluminum, titanium, and the like)bounded by an upper thin-film ARC layer and a bottom thin-film barrierlayer, where at least the top layer is composed of an inorganicdielectric substance. The use of an inorganic dielectric top ARC layeris said to facilitate the use of thinner photoresist layers whilepreserving the integrity of the photoresist pattern for deep sub-micronfeature sizes. (Col. 1, lines 56-58, continuing at Col. 2, lines 1-8.)

All of the references described above pertain to the use of an ARC inthe production of semiconductor devices. The production of semiconductordevices is typically carried out using exposure of a photoresist toblanket radiation through a reticle, to provide efficiency ofproduction. The photoresist exposure time through a reticle is typicallyin the range of seconds to a few minutes. Applicants' invention pertainsto a direct write of a pattern on a photoresist which is used totransfer a pattern to a reticle of the kind which is subsequently usedin semiconductor production. This direct writing of a pattern on thephotoresist takes hours, commonly between about 8 and about 20 hours. Asa result of the time period required for patterning the photoresistwhich is used to fabricate the reticle (as well as possible differencesin the photoresist material), chemical reactions may take place in thephotoresist which affect the critical dimension of the patternedphotoresist. Since the photoresists used for reticle fabrication arechemically amplified photoresists, and the time required for writing thepattern so long, the deflection of imaging radiation off the substrateunderlying the photoresist becomes more critical than it is duringfabrication of a semiconductor device, where photoresist patterning iscarried out by blanket radiation through a reticle for a short timeperiod.

There is currently a need for improvement in the functionality of theARC used in reticle fabrication, so that a reduction in reflectivity isachieved for the radiation wavelengths currently used in the imaging ofreticle fabrication photoresists. In addition, there is a need for ameans of eliminating, or at least significantly reducing, thephotoresist pull back during etching of the chrome layer (or othersimilar radiation blanking layer) to provide better control of thecritical dimension of a patterned reticle.

SUMMARY OF THE INVENTION

We have reduced the critical dimension bias for reticle fabrication.Pattern transfer to the radiation-blocking layer of the reticlesubstrate essentially depends upon transfer from a hard mask rather thanfrom a photoresist. The photoresist pull back which occurs duringpattern transfer to the hard mask is minimal and the change in thecritical dimension between the photoresist pattern and the hard maskpattern is typically less than about 10-12 nm. In addition, when thehard mask material has anti-reflective properties which are tailored tothe imaging radiation wavelength, the reflectivity from the chromesurface is substantially reduced during imaging of the photoresist,which further reduces the change in critical dimension between thedirect write pattern and the pattern transferred to the hard mask. Whenthe selectivity during transfer of the pattern from the hard mask to theradiation-blocking layer is high, typically at least about 5:1 (wherethe radiation-blocking layer etches 5 times faster than the hard mask),this further reduces the critical dimension bias (typically referred toas etch bias) in the pattern transferred to the chrome (or otherradiation-blocking layer). The highest selectivity for theradiation-blocking layer relative to the hard mask, which can beobtained while meeting other requirements for the hard mask, isadvantageous. A combination of the above-described processconsiderations enables a reduction in critical dimension size of thepatterned radiation-blocking layer and provides an improvement in thepattern feature integrity of the patterned radiation-blocking layer. Atypical increase in critical dimension from the size of the direct writepattern radiation to the patterned radiation-blocking layer may be inthe range of about 5% to 7% or less.

In one embodiment of the invention, a hard mask material havinganti-reflective properties may be left on the surface of the chromeafter etching of the chrome. Since the hard mask surface faces thesurface of a photoresist on the semiconductor substrate which ispatterned using the reticle, the presence of the proper anti-reflectiveproperties in the hard mask can be used to reduce the amount ofbounce-back of reflected radiation which occurs during blanket radiationimaging of the semiconductor photoresist through the reticle. By bounceback reflected radiation, it is meant the radiation which reflects offthe semiconductor substrate to the reticle or to other surfaces (betweenthe reticle and the semiconductor substrate) and then back to thesemiconductor substrate photoresist.

In another embodiment of the invention, where a wet etch is used duringfabrication of the reticle, the hard mask material (whether havinganti-reflective properties or not) is removed to prevent contaminationduring the wet etch process. In this embodiment, when a plasma etchantused to remove the hard mask would also etch the reticle base substrate(which is typically quartz), a protective layer is applied to fill atleast a portion of patterned openings through the chrome during removalof the hard mask. This prevents etching of the quartz at the bottom ofthe pattern openings during removal of the hard mask.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C show schematic cross-sectional views of threetypical structures which have been used as a reticle substrate prior topatterning.

FIGS. 1D and 1E are also schematic cross-sectional views, whichillustrate process steps leading to photoresist pull back. Thephotoresist pull back commonly occurs during etching of a chrome (orother radiation-blocking layer) on a reticle substrate, when thestructure of the substrate is one of the kind shown in FIGS. 1A through1C.

FIG. 2A shows a schematic cross-sectional view of an improved reticlefabrication starting structure which is one of the embodiments ofapplicants' invention.

FIGS. 2B through 2D are schematic cross-sectional views which illustratehow chrome pull back (an increase in the opening through the chrome) issubstantially reduced, typically by more than 50% to 70%, using thereticle substrate structure shown in FIG. 2A as compared with thereticle substrate structure shown in FIG. 1A.

FIG. 3A shows a schematic cross-sectional view of a reticle structureincluding a quartz substrate 312, underlying a patternedchrome-containing radiation-blocking layer 314, with an inorganic layerhaving anti-reflective properties 316 on the surface of the patternedradiation-blocking layer 314.

FIG. 3B shows the reticle structure of FIG. 3A inverted into theposition of use in a lithographic stepper.

FIG. 3C shows a schematic cross-sectional view of a reticle structure303 which does not have an inorganic layer which exhibitsanti-reflective properties 316 on the surface of radiation-blockinglayer 314. This provides a comparative example where the finalpatterning radiation 308 d can bounce radiation 311 off the surface 306of a photoresist 320 present on the surface of a semiconductor wafer304. The bounced radiation 311 can reflect off the reticle 303 surface,and produce bounce-back radiation 313 on the surface 306 of photoresist320.

FIG. 3D shows a schematic cross-sectional view of a reticle structure305, of the kind shown in FIGS. 3A and 3B, which does have an inorganiclayer 316 exhibiting anti-reflective properties on the surface ofradiation-blocking layer 314. Final patterning radiation 308 d whichproduces bounced radiation 311, is not reflected back to the surface 306of photoresist 320, because a large portion of the bounced radiation 311is consumed by the inorganic anti-reflective layer 316.

FIGS. 4A through 4E show schematic cross-sectional views of a series ofprocess steps which may be used to remove a hard mask (which may haveanti-reflective properties) overlaying a patterned chrome layer on areticle surface. This procedure may be necessary when a wet etch is tobe carried out on a portion of a radiation-blocking layer or underlyingquartz layer of a phase shifting reticle.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As a preface to the detailed description, it should be noted that, asused in this specification and the appended claims, the singular forms“a”, “an”, and “the” include plural referents, unless the contextclearly dictates otherwise.

In order to obtain patterned reticle structures with smaller sizedcritical dimensions, we have developed a method of reducing the effectof faceting and pull-back of a photoresist used to pattern thestructure. In addition, we have reduced the amount of reflection ofimaging radiation off the radiation-blocking layer of the reticlestructure during direct writing of the pattern onto the photoresist,which further reduces the change in critical dimension between thedirect write pattern and the pattern transferred to the hard mask. Whenthe selectivity during transfer of the pattern from the hard mask to theradiation-blocking layer is high, typically at least about 5:1 (wherethe radiation-blocking layer etches 5 times faster than the hard mask),this further reduces the critical dimension bias (typically referred toas etch bias) in the pattern transferred to the chrome (or otherradiation-blocking layer). A combination of the above-described processconsiderations enables a reduction in critical dimension size of thepatterned radiation-blocking layer and provides an improvement in thepattern feature integrity of the patterned radiation-blocking layer.Further, we have created a reticle structure which can be adjusted toreduce bounced-back, reflected photons off the semiconductor photoresistsurface during semiconductor fabrication.

As mentioned in the Background Art section above, reflections of opticalimaging radiation from underlying materials during direct writing of apattern on the photoresist used to transfer the pattern to theradiation-blocking layer of the reticle frequently creates problemsduring the fabrication of a reticle. Standing waves may be created in anoptically imaged photoresist. The presence of defects in the exteriorshape of the developed photoresist affect the critical dimensions of thereticle pattern, and in particular the resolution of dimensions of thereticle pattern when feature dimensions are in the range of 100 nm andsmaller. It follows that the critical dimensions of the semiconductorstructure fabricated using the reticle are thereby affected.

As previously mentioned, the reticle substrate can be prepared usingapparatus of the kind known in the semiconductor industry for depositionof layers of various materials and for removal of portions of depositedlayers, for example but not by way of limitation.

All processes for patterning a reticle (photomask) can benefit fromapplication of the present method in terms of the critical dimensionsize and pattern integrity which can be achieved in the patternedradiation-blocking layer of the mask, such as a chrome layer. A reticlewith a residual layer of an anti-reflective material (which served as ahard mask during etching of the radiation-blocking layer) isparticularly useful when the reticle is used in combination with anoptical exposure tool during the fabrication of semiconductor devices.With this in mind, the invention is described with reference to use of acontinuous wave direct write laser as the radiation fool and withreference to a chemically amplified DUV photoresist. However, aspreviously mentioned, the benefit of the invention in terms of criticaldimension size of features etched in the radiation-blocking layer of thereticle is also applicable to a direct-write e-beam radiation tool ofthe kind available from Hitachi and Toshiba for the fabrication ofreticles.

In the embodiments of the invention described below, the imaging of thephotoresist material during fabrication of the reticle was carried outusing a direct write continuous wave laser, in particular, a 257 nm or198 nm continuous wave laser direct writing tool available from ETECSystems, Inc., Hillsboro, Oreg. The direct write continuous wave laserwrites, via exposure to optical radiation, a pattern image such as anintegrated circuit pattern, for example and not by way of limitation,onto an unpatterned photoresist coated on the reticle substrate. Thereticle substrate includes a combination of specific layers of the kinddescribed subsequently herein. The exposed photoresist then contains alatent image of the pattern, which is subsequently “developed”, toproduce a patterned photoresist. The patterned photoresist is then usedto transfer the pattern through underlying layers of the reticlesubstrate, to create a patterned reticle. The pattern is typicallytransferred from the photoresist to underlying reticle substrate layersby dry plasma etch techniques, but in some instances a wet etch may beused in combination with the dry etch to achieve particular etchedshapes.

Realization of the desired control over critical dimension (CD) of thepatterned features in the radiation-blocking layer of the reticle dependon a combination of the particular radiation tool which is used and thecomposition of the various layers in the reticle substrate. The presentinvention relates to the selection of and use of the various layers inthe reticle substrate, to provide a smaller dimension CD with improvedpattern integrity across the reticle for a given radiation tool.

Since the reticle fabrication processes of particular interest withrespect to the present invention require the use of a direct writeprocess for irradiating the photoresist, it is important that thephotoresist selected be one which will provide dimensional stability forthe latent image written into the photoresist, both during the writingof the image, and during the time necessary for development of the imageto provide a patterned photoresist. The latent image stability in thephotoresist should be such that there is less than a 5 nm change in theCD during this time period which is typically about 6 hours and mayextend out to as long as about 20 hours, or longer.

The substrate material used for the reticle is typically selected fromthe group of materials including quartz, fluorinated quartz,borosilicate glass, soda lime glass, and combinations thereof. In theembodiments described herein, the substrate used for reticle fabricationwas quartz, which met the requirements shown in Table I below. TABLE IQUARTZ PROPERTIES Quartz Mask Physical Property Condition BlankComposition 100% SiO₂ Thermal Expansion Coefficient 5 (α₅₀ −200° C. ×10⁻⁷) Thermal Annealing Point 1,120° C. Optical Refractive Index 1.46n_(d) Properties Chemical Weight Loss Deionized (DI) water, 0.000%Durabilities 100° C., 1 hour 1/100N HNO₃, 0.000% 100° C., 1 hour 0.17mg/mm² 5% NaOH, 80° C., 1 hourIn addition, the quartz substrate had the following physical properties:a Young modulus of 7.413 kg/mm²; a sheer modulus of 3,170 kg/mm²; aPoisson ratio of 0.18; a Knoop hardness of 615 kg/mm²; and a Lappinghardness of 210 kg/mm².# The electrical properties included a surface resistivity of 1 × 10¹⁹Ω/square and bulk resistivity of 1 × 10¹⁸ Ω/square.

The hard masking material layer may be selected from any of thematerials used in the semiconductor industry as hard masks during aplasma etch process. In some instances, the hard masking material mayhave anti-reflective characteristics. In other instances, it may bedesirable to use a dual layer hard mask, where one layer has noanti-reflective properties and one layer has anti-reflective properties.In considering the selection of a hard masking material, the materialmay need to be able to withstand both a plasma dry etch process and awet etch process, when a phase shifting reticle is being fabricated; orthe hard mask may have to be removed subsequent to dry etch of at leasta portion of the radiation-blocking layer and prior to wet etching.

Typical examples of hard masking materials which provide anti-reflectiveproperties, not by way of limitation, include chrome oxynitride, siliconoxynitride, silicon-rich oxide, silicon-rich nitride, silicon-richoxy-nitride, titanium nitride, molybdenum silicide, and silicon carbide,including: SiC; SiC:H; SiC:O, H; SiC:N, H; and SiC:O, N, H. Plasma etchselectivity for etching the radiation-blocking material relative to theanti-reflective hard masking material should be at least about 5:1 orgreater. The anti-reflective properties of the hard mask need to betailored to protect the particular photoresist in view of the imagingradiation which is being used. By way of example, and not by way oflimitation, the chemically amplified photoresists which are typicallyused for feature sizes of about 150 nm and less incorporate binderpolymers such as methacrylate-containing resins, hydroxy-phenyl-basedresins, aromatic acrylic-based resins and isobornyl-based resins.

Typical examples of hard masking materials which do not provideanti-reflective properties include, not by way of limitation,diamond-like carbon, carbon, tungsten, SiO₂, and Si₃N₄. These materialsare deposited over the radiation-blocking layer of material usingtechniques known in the art, provided the temperature of the substratedoes not rise above about 450° C. during deposition. The hard maskingmaterial selected will depend on the radiation-blocking material intowhich the pattern is to be transferred from the hard mask. Again, theplasma etch selectivity for etching the radiation-blocking materiallayer relative to the hard mask material layer should provide an etchrate for radiation-blocking material layer which is at least about 5times the etch rate for the hard mask material, i.e., the selectivityfor etching the radiation-blocking material should be at least 5:1, andtypically is in the range of about 8:1, although a selectivity of 50:1has been achieved, and higher selectivities may be possible.

EXAMPLE EMBODIMENTS Example One Comparative Example Reticle StartingStructures

FIG. 1A shows a schematic cross-sectional view of a reticle startingstructure 110 of one kind used in the fabrication of a reticle. In thisExample, starting structure 110 was a stack of layers (not shown toscale) which included, from top to bottom, a 5,000 Å thick layer 118 ofa chemically amplified DUV photoresist, DX1100 (available from AZClariant Corp. of Somerville, N.J.); an approximately 200 Å thick layer116 of chrome oxide transitioning to chrome oxynitride; a 750 Å thicklayer 124 of chrome radiation-blocking material; and a siliconoxide-containing substrate 122, which was quartz in this instance.

FIG. 1B shows a schematic cross-sectional view of another reticlestarting structure 120 of the kind used in the fabrication of a reticle.In this Example, starting structure 120 was a stack of layers (not shownto scale) which included, from top to bottom, a 5,000 Å thick layer 128of the chemically amplified DUV photoresist, DX1100; a 470 Å thick layer127 of an organic ARC identified as KRF 17G (available fromAZ/Clariant); a 750 Å thick layer 124 of chrome mask material; and asilicon oxide-containing substrate 122, which was quartz. The organicARC layer 127 was used both as an antireflective coating and to minimizea chemical reaction which occurs in some instances when there is directcontact between a chrome oxide and the photoresist.

FIG. 1C shows a schematic cross-sectional view of a third reticlestarting structure 130 of the kind used in the fabrication of a reticle.In this comparative example, the starting structure was a stack oflayers (not shown to scale) which included, from top to bottom, a 5,000Å thick layer 138 of the chemically amplified DUV photoresist, DX1100; a470 Å thick layer of the organic ARC 237 identified as KRF 17G; a 250 Åthick layer of chromium oxide transitioning to chromium oxynitride(inorganic ARC) 136; a 750 Å thick layer 134 of chrome mask material;and a silicon oxide-containing substrate 132, which was quartz.

All of the example reticle starting structures illustrated in FIGS. 1Athrough 1C suffer from the same problem. They all rely on thephotoresist as the masking material for etching of the chrome maskmaterial. As a result, the thickness of the photoresist layer is 5,000Å, and there is resist pull back which occurs as etching of the chromeprogresses, causing a problem in all of these instances. This problem isillustrated in FIGS. 1D and 1E, using the FIG. 1A reticle startingstructure in the illustrations.

FIG. 1D shows the reticle starting structure of FIG. 1A after thephotoresist 118 has been exposed to the direct write radiation and thendeveloped using the liquid developer recommended by the photoresistmanufacturer. The opening 140 through photomask 118 has a criticaldimension d₁, which could be the width of a trench or the diameter of acontact via, for example. In this instance, the width of the testpattern which was etched was 720 nm. After transferring the opening 140through the underlying layer of chrome oxide/chrome oxynitride, thewidth d₂ of opening 140, as illustrated in FIG. 1E was approximately 780nm to 790 nm. The increase in d₂ over d₁ may be about 60 nm to 70 nm.

As discussed in the Background Art section of the present disclosure, asthe critical dimensions of the patterns in the reticle have becomesmaller, the effect on the width of the critical dimension caused byphotoresist pull back has become a very significant problem.

Example Two Avoiding the Photoresist Pull Back Problem

FIGS. 2A through 2D illustrate the general concept which permits patternetching of the radiation-blocking layer of a reticle without photoresistpull back, and thus without the resulting CD bias problems. FIGS. 2Athrough 2D show schematic cross-sectional views of a reticle fabricationprocess beginning with a starting structure and ending with thepatterned reticle.

FIG. 2A shows the reticle starting structure 200 which consists of, fromtop to bottom, a chemically amplified photoresist layer 218 of the kinddescribed with reference to FIGS. 1A through 1C; the thickness of thephotoresist layer 218 was about 3,000 Å to about 4,000 Å. Underlyingphotoresist layer 218 was a layer of inorganic ARC, Si_(x)O_(y)N_(z) 216which was selected to function as a plasma etching hard mask havinganti-reflective properties. The thickness of the Si_(x)O_(y)N_(z), hardmask layer 216 ranged from about 200 Å to about 500 Å, and was typicallyabout 300 Å. Underlying the Si_(x)O_(y)N_(z) hard mask layer 216 was alayer of chrome 214 having a thickness of about 750 Å which resided onthe surface of a quartz substrate 212.

FIG. 2B shows the reticle starting structure of 2A after imaging anddevelopment to produce an opening having a critical dimension d₄, whichmay be the width of a trench or the diameter of a contact via to betransferred to a semiconductor substrate during use of the reticle, byway of example and not by way of limitation.

In this particular embodiment, the photoresist was UV6, a chemicallyamplified photoresist available from Shipley Company, or was FEP 171, achemically amplified photoresist available from Hoya. The radiationsource used to image the photoresist was an ALTA 4300, 257 nm continuouswave laser direct writing tool, available from ETEC Systems, Inc.Hillsboro, Oreg. The composition of the Si_(x)O_(y)N_(z) hard mask layer216 was such that x ranged from about 0.45 to about 0.55; y ranged fromabout 0.2 to about 0.3; and z ranged from about 0.2 to about 0.3(excluding hydrogen). This particular composition provided an n whichranged from about 1.95 to about 2.1, and a k at 248 nm which ranged fromabout 0.3 to about 0.6, so that a thickness of at least 200 Å ensuredthat radiation from the 257 nm continuous wave laser which was reflectedoff the underlying chrome layer would not pass through theSi_(x)O_(y)N_(z), hard mask layer to the overlying photoresist layer. Inaddition, since the chrome layer to be etched was about 750 Å thick andthe selectivity for the Si_(x)O_(y)N_(z), hard mask layer relative tothe chrome layer was greater than about 7.5:1, the required minimalthickness for the hard mask layer to enable etching through the chromelayer ranged from about 100 Å on the smallest areas to about 200 Å onthe corners. After considering both of these requirements, the thicknessof the Si_(x)O_(y)N_(z) hard mask layer was set at 300 Å, allowing for afactor of safety. Although the photoresist used in the presentembodiment was FEP 171 available from Hoya, or UV6 available fromShipley Company, other similar chemically amplified photoresists such asREAP 122 from TOK, or PEK 130 from Sumitomo/Sumika, or DX1100P fromClariant might have been used, by way of example, and not by way oflimitation. It is advisable to match the nm wave length of the imagingradiation as closely as possible with the nm wave length the photoresistwas designed to work with.

After imaging of the photoresist, the photoresist was developed in themanner recommended by the manufacturer of the photoresist. The criticaldimension d₄ was the test pattern dimension in the range of about 720nm.

In the case when there is a chrome-oxynitride ARC layer present beneaththe Si_(x)O_(y)N_(z) ARC layer, then the Si_(x)O_(y)N_(z) ARC layershould be tuned closer to a k=0.3 at the 257 nm exposure wavelength.This is achieved by reducing (x) to the lower limit around 0.4-0.45. Inthe case of chrome without a chrome oxynitride ARC surface layer, theSi_(x)O_(y)N_(z) should be tuned closer to a k=0.5 to 0.6 at theexposure wavelength. This is achieved by increasing (x) to the upperlimit around 0.5 up to 0.6.

Silicon oxynitride can not be used as an electron beam ARC. For ane-beam ARC, a conducting layer such as α-Si or α-C should be used.

The Si_(x)O_(y)N_(z) ARC/hard mask layer was deposited using plasmaenhanced chemical vapor deposition (PECVD). The PECVD was carried out ina parallel plate capacitively coupled plasma processing apparatus. Theprecursors for the PECVD were SiH₄, N₂O, and He, which were used in theproportions shown in Table II, below, depending on the desired values ofx, y, and z. The pressure in the CVD chamber ranged from about 3 Torr toabout 9 Torr, with good results obtained at 5 Torr. For this processchamber, the overall flow rate of the reactant gases ranged from about4,000 sccm to about 4,300 sccm, with specific amounts of each gas shownin Table II below. The plasma source power ranged from about 0.25 W/cm²to about 1 W/cm², where the cm² refers to the surface area of thereticle substrate upon which the hard mask layer was deposited. Nobiasing power was applied to the substrate. The temperature of thecathode (support pedestal) underlying the reticle substrate ranged fromabout 250° C. to about 400° C., with a resulting reticle temperaturebeing in the range of about 210° C. to about 360° C. Operation of thePECVD deposition process at lower temperatures results in a reduction inthe selectivity of the Si_(x)O_(y)N_(z) layer relative to theradiation-blocking layer. With respect to a chrome radiation-blockinglayer, a 400° C. cathode temperature did not appear to affect theunderlying chrome. No roughness of the etched chrome line appeared afteretch, which roughness would have been attributed to crystallization orgrain growth or similar change in the chrome due to exposure to thetemperature used during PECVD deposition of the Si_(x)O_(y)N_(z) layer.TABLE II PROCESS CONDITIONS FOR PECVD Si_(x)O_(y)N_(z) Currently BestProcess Condition General Range Preferred Range Known Range Total GasFlow  4190 ± 50%  4190 ± 20%  4190 ± 10% (sccm) SiH₄ (sccm)   110 ± 50%  110 ± 10%   110 ± 10% N₂O (sccm)   280 ± 50%   280 ± 50%   280 ± 10%Helium (sccm) 3,800 ± 50% 3,800 ± 50% 3,800 ± 10% Substrate 150 to 450250 to 425 350 to 400 Temperature (° C.) Process Chamber 150 to 450 250to 425 350 to 400 Temperature (° C.) Process Chamber    5 ± 50%    5 ±20%    5 ± 10% Pressure (Torr) Source Power  0.4 ± 100%  0.4 ± 25%  0.4± 10% (W/cm²)The spacing between the substrate upper surface and the face plate inthe 8 inch wafer PECVD chamber used for film deposition was about 350mils (8.9 mm) to 400 mils (10.2 mm).The processing conditions described above were designed to provide aSi_(x)O_(y)N_(z) film having a refractive index, n, at exposure λ (257nm) in the range of about 2.0 ± 30%, and typically about 2.0 ± 20%, withthe thickness of the film layer ranging from about 100 Å to 1,000 Å,# and typically about 250 Å to about 300 Å for use in combination withthe underlying chrome layer, in accordance with the relationship betweenthe optical properties (n, k, and d) required for total phase-shiftcancellation, where n is the refractive index, k is the extinctioncoefficient, and d is the thickness of the film.The processing conditions described above were designed to provide aSi_(x)O_(y)N_(z) film having an extinction coefficient, k, at exposure λ(257 nm) in the range of about 0.4 ± 50%, and typically 0.4 ± 20%, withthe thickness of the film layer ranging from 100 Å to 1,000 Å,# and typically about 250 Å to about 300 Å for use in combination withthe underlying chrome layer.

As illustrated in FIG. 2C, subsequent to patterning of the FEP 171photoresist 218, the photoresist was used to transfer the patternthrough the underlying Si_(x)O_(y)N_(z), hard mask layer 216 using aplasma etch process, where the plasma source gas used to generate theetchant plasma consisted essentially of CF₄ and CHF₃, or consistedessentially of SF₆ and helium. Either of these source gases providedgood results. When the CF₄/CHF₃ plasma source gas was used, typicallythe volumetric ratio of CF₄ to CHF₃ ranged from about 1:10 to about 2:1,with good results achieved at about 1:3. When the SF₆ and helium plasmasource gas was used, the volumetric ratio of SF₆ to helium was about0.02:1 to about 0.05:1, with good results achieved at about 0.033:1. Thepressure in the etch chamber typically ranged from about 1 mTorr toabout 10 mTorr, with good results achieved at about 3 mTorr for theCF₄/CHF₃ plasma and at about 5 mTorr for the SF₆/helium plasma. The etchprocess was carried out in a TETRA II® etch chamber, which is a DPS™etch chamber available from Applied Materials, Inc. of Santa Clara,Calif.

In this etch chamber, the plasma source gas flow rate ranged from about20 to about 100 sccm, and was typically about 40 sccm. The plasma sourcepower applied ranged from about 200 W to about 700 W, with good resultsbeing achieved at about 250 W. The plasma density in the etch chamberranged from about 1×10¹¹ to about 1×10¹², i.e. a high density plasma wasused. The reticle substrate was biased at a bias power ranging fromabout 10 W to about 200 W. For the CF₄/CHF₃ plasma source gas etchchemistry, a bias power of about 70 W provided good results. For theSF₆/helium plasma source gas etch chemistry, a bias power of about 50 Wprovided good results. The temperature of the cathode beneath thereticle substrate was typically about 20° C., and the chamber walltemperature was typically about 65° C.

The substrate rested on an anodized aluminum surface of the biasedcathode and was held in place by gravity. A capture ring surrounded thesubstrate and helped prevent plasma etchant from reaching the backsideof the reticle substrate. A DPS™ etch chamber, like the TETRA II® etchchamber, permits separate power application for plasma generation andfor substrate biasing (which is commonly referred to as a DecoupledPlasma Source (DPS)). Separate application of power for plasmageneration and power for substrate biasing permits separate control ofthe plasma density and the attractive forces (DC voltage) generated onthe surface of the substrate.

The Si_(x)O_(y)N_(z), hard mask 216 was etched through providing acritical dimension d₅ of about 733 nm, providing a difference betweenthe d₄ critical dimension of the photoresist and d₅ critical dimensionof the Si_(x)O_(y)N_(z), hard mask of only about 13 nm. The residualportion of photoresist layer 218 which remains after etching through theSi_(x)O_(y)N_(z) hard mask 216 may be removed prior to etching of thechrome layer 214 if the photoresist material tends to deform duringetching of the chrome layer 214. However, if the photoresist used doesnot deform in a manner which affects the etch profile of the openingetched into the chrome layer 214, it may be advantageous to leaveresidual photoresist layer 218 in place, to be consumed during theetching of chrome layer 214, as this helps reduce the effect of any “pinholes” (not shown) in the Si_(x)O_(y)N_(z) hard mask 216, due to theinitial thickness of hard mask 216 typically being less than about 400Å.

FIG. 2D illustrates the reticle after plasma etch through chrome layer214. The chrome was etched in the same etch process chamber as describedabove with reference to etching the Si_(x)O_(y)N_(z), hard mask. Theplasma source gas used for generation of the plasma etchant was chlorinein the form of Cl₂ and oxygen in the form of O₂. Other gases which areinert may be added to the plasma source gas, such as helium, neon,argon, and krypton, by way of example and not by way of limitation. Whena Cl₂/O₂ plasma source gas was used, typically the volumetric ratio ofCl₂ to O₂ ranged from about 20:1 to about 1:1.2, with good resultsachieved at about 10:1. When helium was added as an inert gas, thevolumetric ratio of helium relative to oxygen ranged from about 15:1 toabout 1.2:1. The pressure in the etch chamber typically ranged fromabout 3 mTorr to about 10 mTorr, with good results achieved at about 4mTorr.

In the TETRA II® etch chamber, the overall plasma source gas flow rateranged from about 100 to about 500 sccm, and was typically about 400sccm. The plasma source power applied ranged from about 300 W to about600 W, with good results being achieved at about 350 W. The plasmadensity in the etch chamber ranged from about 1×10¹¹ e⁻/cm² to about1×10¹² e⁻/cm², i.e. a high density plasma was used. The reticlesubstrate was biased at a bias power ranging from about 0 W to about 200W. For the Cl₂/O₂ plasma source gas etch chemistry, a bias power ofabout 15 W provided good results. The temperature of the cathode beneaththe reticle substrate was typically about 20° C., and the chamber walltemperature was typically about 65° C.

The chrome radiation-blocking layer was etched through providing acritical dimension d₆ of about 760 nm, and the difference between the d₄critical dimension of the photoresist and d₆ critical dimension of thepatterned chrome radiation-blocking layer was only about 40 nm, comparedwith the 60 nm to 70 nm which was observed when the chrome was etchedusing a photoresist mask. This significant improvement in the etch biasbetween the developed photoresist critical dimension and the patternedradiation-blocking layer critical dimension enables the production of areticle having smaller feature sizes. Although the test pattern etchedhere was a 720 nm test pattern, a similar proportional improvement inetch bias is expected to occur for the smaller pattern features, in the110 nm range, for example.

When the hard mask used to pattern the chrome layer is a material suchas diamond-like carbon, the plasma source gas used to generate theplasma for etching the diamond-like carbon material may be oxygen andhelium, for example. Typically, the volumetric ratio of oxygen to heliumranges from about 1:1 to about 1:10. The pressure in the etch chambercommonly ranges from about 3 mTorr to about 15 mTorr, with good resultsachieved at about 8 mTorr in a TETRA® II etch chamber. A plasma sourcegas flow rate of about 20 sccm to about 100 sccm is used, with a typicalflow rate being about 40 sccm. The plasma source power applied is about200 W to about 700 W. The plasma density in the chamber ranges fromabout 1×10¹¹ e⁻/cm² to about 1×10¹² e⁻/cm². The reticle substrate isbiased at a bias power of about 20 W to about 70 W. The temperature ofthe cathode beneath the reticle substrate is typically about 20° C., andthe chamber wall temperature is typically about 65° C.

Example Three Advantage of a Reticle Having an ARC over the PatternedRadiation-Blocking Layer

FIGS. 3A through 3D illustrate schematic cross-sectional views whichshow the advantages of a reticle structure where a hard mask havingantireflective properties is present over the surface of a patternedchrome-containing layer (or other radiation-blocking layer) duringimaging of a photoresist on a semiconductor wafer using the reticle.This feature is helpful when imaging of the photoresist is with opticalradiation.

FIG. 3A shows a schematic cross-sectional view of a reticle structure305 including, from bottom to top, a quartz substrate 312, underlying apatterned chrome-containing radiation-blocking layer 314, with aninorganic layer having anti-reflective properties 316 present on theupper surface of the patterned radiation-blocking layer 314. Thisstructure is of the kind shown in FIG. 3D above, the fabrication ofwhich is described in detail with reference to FIG. 3D.

FIG. 3B shows the reticle structure of FIG. 3A inverted into theposition in which it is used in a lithographic stepper, for way ofexample, and not by way of limitation with respect to the lithographicexposure tool.

FIG. 3C shows a schematic cross-sectional view of a reticle structure303 which does not have an inorganic layer which exhibitsanti-reflective properties 316 on the surface of radiation-blockinglayer 314. The radiation source 307 produces initial radiation 308 a,which passes through a condenser 301 and provides imaging radiation 308b. The imaging radiation 308 b passes through reticle structure 303 andprovides patterned imaging radiation 308 c. The patterned imagingradiation 308 c passes through a reduction lense 318 to produce thefinal patterning radiation 308 d which reaches the surface 306 ofphotoresist 320. Final patterning radiation 308 d can bounce radiation311 off the surface 306 of photoresist 320 present on a semiconductorwafer 304, supported by pedestal 302. The bounced radiation 311 canreflect off the reticle 303 surface, and produce bounce-back radiation313 on the surface 306 of photoresist 320.

FIG. 3D shows a schematic cross-sectional view of a reticle structure305, of the kind shown in FIGS. 3A and 3B, which does have an inorganiclayer with anti-reflective properties 316 on the surface ofradiation-blocking layer 314. Final patterned radiation 308 which passedthrough reticle structure 305 which bounces back to the inorganic layer316 which has anti-reflective properties is not reflected back to thesurface 306 of the photoresist 320. This enables a better defined imagein the photoresist 320 and improves the uniformity of the image in thephotoresist 320 across the semiconductor wafer 304.

Example Four Removal of Inorganic Hard Mask or ARC From the Surface ofthe Radiation-Blocking Layer

There are instances when it is desired to remove residual hard masklayer or ARC layer from the surface of the patterned radiation-blockinglayer of the reticle without harming the basic substrate of the reticle(the quartz or borosilicate glass, or soda lime glass, for example). Ifthe residual hard mask layer or residual inorganic ARC/hard mask layercontains a material which is common to the basic substrate material,then removal of the hard mask layer or ARC/hard mask layer isproblematic. An example of this would be the removal of a siliconoxynitride ARC/hard mask layer when the base substrate layer of thereticle which is exposed through a patterned radiation-blocking layercontains silicon, i.e. is quartz.

Removal of residue of such an ARC/hard mask layer may be necessary whenthe reticle is a phase shifting reticle. There are generally two kindsof phase shifting reticles. A first kind is referred to as an attenuatedphase shift reticle, which employs a molybdenum/silicon (MoSi) layeroverlying the chromium radiation blocking layer. A second kind isreferred to as an alternating phase shift reticle, which employs etchingthrough areas of the quartz base substrate layer to varying depths.Fabrication of each of these phase shifting reticles may require the useof a wet etch process. As a result, the removal of hard mask residuefrom the surface of the patterned radiation-blocking layer is necessary,so that this residue will not lift off during the wet etch process,depositing contamination of the surfaces of the reticle structure.

FIGS. 4A through 4E show schematic cross-sectional views of a series ofprocess steps which may be used to remove a hard mask (which may haveanti-reflective properties) overlaying a patterned chrome layer on areticle surface.

FIG. 4A shows a schematic cross-sectional view of a reticle substrate400 including, from bottom to top, a quartz base substrate layer 412, apatterned overlying chrome layer 414 having a thickness of about 750 Å,and a layer of Si_(x)O_(y)N_(z) antireflective coating/hard mask layer416 having a thickness of about 200 Å to about 300 Å. The patternedopening 418 in the chrome layer 414 continues entirely through chromelayer 414 to the upper surface 420 of quartz base substrate layer 412.

To permit plasma etch removal of the layer of Si_(x)O_(y)N_(z)antireflective coating/hard mask 416 without damage to the surface 420of quartz base substrate layer 412, it is necessary to apply aprotective material 422 over the surface of reticle substrate 412,filling opening 418. This is shown in FIG. 4B. The layer of protectivematerial 422 may be applied by any of the means of applying additivelayers during semiconductor processing. However, an preferred method ofapplying protective material 422 is by spin-on techniques of the kindused for an organic spin-on layer such as a photoresist. Therequirements for protective layer 422 are easy and inexpensiveapplication and good selectivity for etch relative to hard masking layer416 (which in this example, and not by way of limitation, isSi_(x)O_(y)N_(z) antireflective coating/hard mask.)

Subsequent to application of protective layer 422, which is preferablyan organic material, an etch-back process is carried out to expose thesurface of the Si_(x)O_(y)N_(z) antireflective coating/hard mask layerto be removed. This step is shown in FIG. 4C. The etch back processleaves enough organic material covering the quartz base layer 412 toprotect this layer during removal of the Si_(x)O_(y)N_(z) antireflectivecoating/hard mask layer. Typically the etch chemistry for the plasmaetch back of the organic material provides for use of a plasma sourcegas comprising oxygen, nitrogen and hydrogen. Plasma etch processes foretching organic materials such as photoresists using this chemistry areknown in the art.

Once the Si_(x)O_(y)N_(z) antireflective coating/hard mask layer hasbeen exposed, as shown in FIG. 4C, this layer is removed using a CF₄ andoxygen plasma etch (or other similar fluorine-containing etch known inthe art for the removal of silicon oxynitride), to produce the structureshown in FIG. 4D.

In the final step of the process, the spin-on organic material ofprotective layer 420 is removed either using a plasma etch where theplasma is generated from a source gas comprising a mixture of oxygen,nitrogen and hydrogen, or by using a wet etch solution known in the artfor removal of organic material. It is also possible to use an ashingprocedure of the kind known in the art for removal of the protectiveorganic material.

The above described exemplary embodiments are not intended to limit thescope of the present invention, as one skilled in the art can, in viewof the present disclosure expand such embodiments to correspond with thesubject matter of the invention claimed below.

1. A method of reducing critical dimension bias during fabrication of areticle, comprising: (a) providing a reticle starting substratecomprising a base substrate layer, a radiation-blocking layer overlyingsaid base substrate layer, at least one hard mask layer overlying saidradiation-blocking layer, and a chemically amplified photoresist layeroverlying the hard masking layer; (b) direct writing a latent image intosaid chemically amplified photoresist layer; (c) developing saidphotoresist containing said latent image into a patterned photoresist;(d) transferring a pattern from said photoresist to said at least onehard mask layer using a plasma etch technique; and (e) transferring saidpattern from said at least one hard mask layer to saidradiation-blocking layer using a plasma etch technique, whereby theincrease in a critical dimension of said radiation-blocking layer afterpatterning from said developed photoresist critical dimension is about7% or less.
 2. A method in accordance with claim 1, wherein said atleast one hard mask layer exhibits anti-reflective properties capable ofsubstantially reducing reflection of optical radiation off a surface ofsaid radiation-blocking layer.
 3. A method in accordance with claim 1,wherein said at least one hard mask layer exhibits two layers, where afirst hard mask layer which is in contact with said radiation-blockinglayer has anti-reflective properties capable of substantially reducingreflection of optical radiation off a surface of said radiation-blockinglayer, and a second hard mask layer overlying said first layer does nothave such anti-reflective properties.
 4. A method in accordance withclaim 1, wherein said base substrate layer is selected from the groupconsisting of quartz, borosilicate glass, soda lime glass, andcombinations thereof.
 5. A method in accordance with claim 2 or claim 3,wherein said base substrate layer is selected from the group consistingof quartz, borosilicate glass, soda lime glass, and combinationsthereof.
 6. A method in accordance with claim 1, wherein said chemicallyamplified photoresist includes a resin selected from the groupconsisting of methacrylate-containing polymer, a novolak, ahydroxy-phenyl polymer, an aromatic acrylic polymer, anisobornyl-containing polymer, and combinations thereof.
 7. A method inaccordance with claim 2 or claim 3, wherein said chemically amplifiedphotoresist A method in accordance with claim 1, wherein said chemicallyamplified photoresist includes a resin selected from the groupconsisting of methacrylate-containing polymer, a novolak, ahydroxy-phenyl polymer, an aromatic acrylic polymer, anisobornyl-containing polymer, and combinations thereof.
 8. A method inaccordance with claim 1, wherein said pattern is direct written on saidphotoresist using a continuous wave laser operating at a wavelengthranging from about 198 to about 257 nm.
 9. A method in accordance withclaim 2 or claim 3, wherein said pattern is direct written on saidphotoresist using a continuous wave laser operating at a wavelengthranging from about 198 to about 257 nm.
 10. A method in accordance withclaim 1, wherein said at least one hard mask exhibits anti-reflectiveproperties and is selected from the group consisting of chromeoxynitride, silicon oxynitride, silicon-rich oxide, silicon-richnitride, silicon-rich oxy-nitride, titanium nitride, molybdenumsilicide, and silicon carbide, including: SiC; SiC:H; SiC:O, H; SiC:N,H; and SiC:O, N, H.
 11. A method in accordance with claim 2 or claim 3,wherein said hard mask having anti-reflective properties is selectedfrom the group consisting of chrome oxynitride, silicon oxynitride,silicon-rich oxide, silicon-rich nitride, silicon-rich oxy-nitride,titanium nitride, molybdenum silicide, and silicon carbide, including:SiC; SiC:H; SiC:O, H; SiC:N, H; and SiC:O, N, H.
 12. A method inaccordance with claim 10, wherein said hard mask having anti-reflectiveproperties is deposited using plasma enhanced chemical vapor deposition.13. A method in accordance with claim 11, wherein said hard mask havinganti-reflective properties is deposited using plasma enhanced chemicalvapor deposition.
 14. A method in accordance with claim 1, wherein saidat least one hard mask does not exhibit anti-reflective properties andis selected from the group consisting of diamond-like carbon, siliconoxide, silicon, carbon, tungsten, and Si₃N₄.
 15. A method in accordancewith claim 3, wherein said second hard mask which does not haveanti-reflective properties is selected from the group consisting ofdiamond-like carbon, silicon oxide, silicon, carbon, tungsten, andSi₃N₄.
 16. A method of reducing critical dimension bias duringfabrication of a semiconductor structure using a reticle, comprising:(a) providing a reticle comprising at least one hard mask layer havinganti-reflective properties, which hard mask layer having saidanti-reflective properties overlies a radiation-blocking layer, whichoverlies a base substrate layer; and (b) exposing an imaging layer on asurface of said semiconductor structure to radiation passed through saidreticle.
 17. A method in accordance with claim 16, wherein said at leastone hard mask layer which exhibits antireflective properties is capableof substantially reducing reflection of optical radiation off a surfaceof said semiconductor substrate.
 18. A method in accordance with claim16, wherein said at least one hard mask layer consists of two layers,where a first hard mask layer which is in contact with saidradiation-blocking layer has anti-reflective properties capable ofsubstantially reducing reflection of optical radiation off a surface ofsaid radiation-blocking layer, and a second hard mask layer overlyingsaid first layer does not have such anti-reflective properties.
 19. Amethod in accordance with claim 17, wherein said at least one hard maskexhibits anti-reflective properties and is selected from the groupconsisting of is selected from the group consisting of chromeoxynitride, silicon oxynitride, silicon-rich oxide, silicon-richnitride, silicon-rich oxy-nitride, titanium nitride, molybdenumsilicide, and silicon carbide, including: SiC; SiC:H; SiC:O, H; SiC:N,H; and SiC:O, N, H.
 20. A method in accordance with claim 18, whereinsaid hard mask having anti-reflective properties is selected from thegroup consisting of is selected from the group consisting of chromeoxynitride, silicon oxynitride, silicon-rich oxide, silicon-richnitride, silicon-rich oxy-nitride, titanium nitride, molybdenumsilicide, and silicon carbide, including: SiC; SiC:H; SiC:O, H; SiC:N,H; and SiC:O, N, H.
 21. A method in accordance with claim 19 or claim20, wherein said hard mask having anti-reflective properties isdeposited using plasma enhanced chemical vapor deposition.
 22. A methodin accordance with claim 17, wherein said at least one hard mask whichdoes not exhibit anti-reflective properties is selected from the groupconsisting of diamond-like carbon, silicon oxide, silicon, carbon,tungsten, and Si₃N₄.
 23. A method in accordance with claim 18, whereinsaid second hard mask which does not have anti-reflective properties isselected from the group consisting of diamond-like carbon, siliconoxide, silicon, carbon, tungsten, and Si₃N₄.
 24. A method in accordancewith claim 16 or claim 18, wherein said hard mask which does not exhibitanti-reflective properties is deposited using plasma enhanced chemicalvapor deposition.